The invention relates to an electric wrench, more particularly, to an electric wrench which uses a low power motor but instantly reaches high rotation speed, so that it can accomplish a given task, that is tightening or loosening a screw or nut, as effectively as models with larger motors.
Referring to FIGS. 1 and 2, a conventional electric wrench includes a housing H enclosing a motor A with an axle A2; a transmission gear assembly B associated with the axle of the motor A; the base end of a drive shaft C fixedly attached to the gear assembly B, a pair of grooves C2 on the other end of the drive shaft C, into which buffing balls D2 can be disposed; a drive sleeve E having a pair of opposed grooves E1 inside its bore and sleeved over the drive shaft, the buffing balls D2 engaging the two pairs of grooves of the drive sleeve and the drive shaft, the drive sleeve further having a pair of engaging ends extending axially therefrom; the base end of a driven shaft F having two engaging ends F1, being adapted to engage with the pair of engaging ends E2 of the drive sleeve, the top end of said driven shaft having a throughbore F2 in which a tool can be inserted, and a throughhole F3 passing through the through bore F2 adjacent to the top end of the same; a coil spring D1 disposed around the drive shaft urging the drive sleeve to the driven shaft so that the two pairs of engaging ends can engage each other; a clamping means G sleeved on the front end of the driven shaft F and clamping said tool, which exists outside of the front portion H2 of the housing H, as shown in FIG. 2.
In order to achieve high torsion and high speed, the conventional wrench has to use a motor of high power. This is only because at the beginning or end of a given task, high torsion is required to overcome increased friction at that stage. However, the intermediate stage between the beginning and the end of securing operation, does not require such high power, so conventional electric wrenches waste energy.